FIGURE 2.

Local unwinding of collagen fibrils. Contact mode AFM error signal images of digital tendon collagen fibrils (scale bar, 500 nm). (a) A fibril is somewhat unwound (arrowed) but still displays axial D-banding. (b) The fibril is more unwound, has the appearance of a rope with linear substructures, and D-banding is less apparent. (c) The arrows indicate the presence of the “birdcaging” phenomenon along the length of the fibril, as seen in ropes or hawsers that are put under compressive forces or reverse twist. (d) Some of these regions (circled) display a multi-strand subfibrillar structure with at least three strands.